250 ON SOME BLOWPIPE-REACTIONS. 



cliarcoal ; but if tlie metal be fused on a cupel, or on a piece of thin 

 porcelain or other non-reducing body, the evolved fumes are almost 

 wholly of a brownish-colour, and the deposit is in great part brownish- 

 black. It would appear, therefore, to consist of TIO^, rather than of 

 a mixture of metal and oxide. On the cupel, thallium is readily oxi- 

 dized and absorbed. It might be employed, consequently, as suggested 

 by Crookes, in place of lead, in cupellation ; but to effect the absorp- 

 tion of copper or nickel a comparatively large quantity is required. 

 When fused on porcelain, the surface of the support is strongly 

 attacked by the formation of a silicate, which is deep-red whilst hot 5 

 and pale-yellow on cooling. 



The tei'oxide, as stated by Crookes, evolves oxygen when heated, 

 and becomes converted into TIO. The latter compound is at once 

 reduced on charcoal, and the reduced metal is rapidly volatilized with 

 brilliant green coloration of the flame. The chloride produces the 

 same reaction, by which the green flame of thallium may easily be 

 distinguished from the green copper-flame, the latter, in the case of 

 cupreous chlorides, becoming changed to azure-blue. With borax 

 and phosphor-salt, thallium oxides form colourless glasses, which 

 become gray and opaque when exposed for a short time to a reducing 

 flame. With carb.-soda, they dissolve to some extent, but on charceal 

 a malleable metallic globule is obtained. The presence of soda, 

 unless in great excess, does not destroy the green coloration of the 

 flame. 



Thallium alloys more or less readily with most other metals before 

 the blowpipe. With platinum, gold, bismuth, and antimony, respec- 

 tively, it forms a dark-gray brittle globule. With silver, copper, or 

 lead, the button is malleable. With tin, thallium unites readily, but 

 the fused mass immediately begins to oxidize, throwing out excres- 

 cences of a dark colour, and continuing in a state of ignition until 

 the oxidation is complete. In this, as in other reactions, therefore, 

 the metal much resembles lead. 



II.— ON THE OPALESCENCE PRODUCED BY SILICATES IN 

 PHOSPHOR-SALT. 



It is well-known that most silicates when fused with phosphor-salt 

 are only partially attacked : the bases, as a rule, gradually dissolving 

 in the flux, whilst the silica remains in the form of a flocculent mass 

 technically known as a " silica-skeleton." Yery commonly, almost 



